Utilisation of potassium rich crop residues for retention of potassium in lateritic soil

Abstract

Potassium is a versatile vital nutrient for regular plant and animal growth and development. It is regarded as a "quality nutrient" because of its multifunctional role in metabolism. Kaolinite clay minerals prevalent in lateritic soils of Kerala, have lower activity and prevent the retention of available forms of potassium. Potassic fertilisers are often overlooked in fertiliser schedules due to their high unsubsidized cost. There are some K rich organic sources that are ignored by the farmers and are left or burnt in the soil. The utilisation of organic K resources like rice straw and plantain compost made from banana wastes are regarded good alternatives for synthetic potassic fertilisers. The present investigation consisted of three experiments viz., (i) assessment of decomposition dynamics of rice straw and its K release, (ii) K adsorption study on rice straw and prepared plantain compost and (iii) an incubation study in lateritic soil with different sources of potassium. The decomposition rate of rice straw has increased with the period of its incubation and it showed only a partial decomposition of 51.9 % at 90 days due to the presence of more amount of lignin, cellulose and hemicellulose content which takes more time for its degradation. The potassium release rate increased to 84.28 % at 90 days of its decomposition. The adsorption study on rice straw with different levels of KCl solution at different periods of decomposition revealed that as the solution concentration increased, the quantity of K adsorbed on rice straw also increased along with the increase in incubation period. Similarly, plantain compost that was prepared using vermi technology also showed an increased trend in the value of quantity of K adsorbed on compost as the KCl concentration increased. Because of its smaller particle size and larger surface area, plantain compost has stronger adsorption and buffer power than rice straw. Rice straw with potash (T1), plantain compost with potash (T2), wood ash, FYM with potash (T3), rice straw with lime and potash (T4), plantain compost with lime and potash (T5), wood ash, FYM with lime and potash (T6), lime and potash (T7), potash alone (T8), and absolute control (T9) treatments were used in the incubation study. The physico-chemical characteristics of soil such as pH, EC, organic carbon, available N, P, Ca, Mg, S, Fe, Cu, Zn, and Mn were determined at initial and final days of incubation. Data on the different fractions of soil K indicated that the treatment containing rice straw with lime and Muriate of potash (T4) showed the higher value of total K, exchangeable K and non-exchangeable K after 90 days of incubation. The reason might be that the presence of more inter planar sites in rice straw has trapped the K+ ions in fixed form since the material is not completely decomposed. At the same time incorporation of rice straw has enhanced the CEC of the soil thus enhancing greater adsorption of exchangeable K from unavailable forms by mass effect. The current study showed that combining organic K resources with lime and K fertilisers resulted in significant increases in soil K fractions. Integrated application of rice straw with lime and K fertiliser can be considered as the best method for long-term cultivation because it has the ability to retain and release more K, particularly nonexchangeable, exchangeable, and total K, allowing for continuous uptake of K by the crops for normal growth and development. The usage of plantain compost in combination with lime and Muriate of potash has resulted in increased availability of K as well as micronutrients by maintaining favourable pH.